1. Field of the Invention
The present invention relates to a method for manufacturing a direct bonded SOI (Silicon On Insulator) wafer by bonding two silicon wafers via a silicon oxide film, a so-called direct bonded SOI wafer manufacturing method and a direct bonded SOI wafer manufactured by the method. The present invention relates more particularly to a method for manufacturing a direct bonded SOI wafer in which the entire buried oxide film layer is covered and is not exposed and a direct bonded SOI wafer manufactured by the method.
2. Description of the Related Art
With high integration, high performance, multi-functions and high reliability of a semiconductor integrated circuit, a dimension of a pattern has become increasingly finer. With this, an SOI wafer having a thin-filmed SOI layer without a defect on a wafer surface layer to be a device-forming area with an oxide film layer between them is in demand. As a method for manufacturing this type of SOI wafer, there are methods such as a bonding method in which a thin-filmed active wafer is bonded to a support wafer for the creation thereof and the SIMOX (Separation by Implanted Oxygen) method in which an oxygen ion is implanted from a wafer surface to form a BOX layer in an area at a predetermined depth from the wafer surface.
Among them, with a method for manufacturing SOI wafer using a bonding method, as shown in FIG. 7(a), in order to obtain an SOI wafer 4, a semiconductor wafer 1 and a support wafer 2 are bonded together via an oxide film 3, and the semiconductor wafer 1 is formed to a desired thickness to be made into a single-crystal silicon layer. End edges 3a, 3a in a buried silicon oxide layer 3 of the obtained SOI wafer 4 are not buried but exposed on the side face. Therefore, in the semiconductor device manufacturing process, the exposed end edges 3a, 3a of the oxide film 3 are removed at the etching by a fluorinated acid solution or the like. As a result, as shown in FIG. 7B, end faces 1a, 1a of a single crystal silicon layer 1 corresponding to an upper layer are extended in the apprentice state. These extended portions 1a, 1a have a small thickness and a low mechanical strength, and they can be cracked or separated during various subsequent processing processes. Silicon pieces generated by this might become particles, adhere to the surface of the single crystal silicon layer 1 in the active area and cause a pattern defect or other defects in laminated films, which results in a problem that the product yield is lowered. Also, in the case of epitaxial growth, poly-silicon grows in an exposed oxide film portion, which results in a problem that particles are generated in the fluorinated acid processing process.
As a measure to improve these problems, a semiconductor substrate manufacturing process is known wherein, after removing a periphery portion of an SOI semiconductor substrate manufactured using the bonding method, a silicon oxide film layer interposed between an upper layer portion and a lower layer portion of the substrate is covered by a protective coating against a silicon oxide-film soluble agent at least on the side face of the substrate and then, an unnecessary portion of the coating is removed (See the Patent Document 1, for example).
Japanese Unexamined Patent Application No. 4-129267 (claim 5, p. 3, lower right column, 1. 12 to p. 5, upper right column, 1. 18 and FIGS. 2(A) to (M))
However, with the method disclosed in the Patent Document 1, there is a problem that the manufacturing cost is raised by increase in the number of processes since a process for covering the end edges from which the buried oxide films are exposed after bonding by a gas phase epitaxy and a process for removing a film formed by the gas phase epitaxy are added to processes generally performed in the bonding method.
An object of the present invention is to provide a method for manufacturing a direct bonded SOI wafer in which the entire buried oxide film layer is covered and not exposed and a direct bonded SOI wafer manufactured by the method.
Another object of the present invention is to provide a method for manufacturing a direct bonded SOI wafer which can reduce the manufacturing cost and a direct bonded SOI wafer manufactured by the method.